<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script>
    function getLongest(s = ''){
      if (s.length <= 1) return s.length
      let max = 0  // 最长长度

      for(let i = 0; i < s.length; i++){
        let subStr = s[i]
        for(let j = i + 1; j <= s.length; j++){
          if(j === s.length){
           max = Math.max(max,subStr.length)
          } else if (subStr.includes(s[j])){
            max = Math.max(max,subStr.length)
            break
          } else {
            subStr += s[j]
          }
        }
        return subStr
      }
    }
    console.log(getLongest('absca'));
  </script>
</body>
</html>